Last visit was: 12 Dec 2024, 00:34 It is currently 12 Dec 2024, 00:34
Close
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
User avatar
stonecold
Joined: 12 Aug 2015
Last visit: 09 Apr 2024
Posts: 2,261
Own Kudos:
3,297
 [2]
Given Kudos: 893
GRE 1: Q169 V154
GRE 1: Q169 V154
Posts: 2,261
Kudos: 3,297
 [2]
1
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
User avatar
mikemcgarry
User avatar
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Last visit: 06 Aug 2018
Posts: 4,485
Own Kudos:
29,380
 [1]
Given Kudos: 130
Expert reply
Posts: 4,485
Kudos: 29,380
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
stonecold
Joined: 12 Aug 2015
Last visit: 09 Apr 2024
Posts: 2,261
Own Kudos:
Given Kudos: 893
GRE 1: Q169 V154
GRE 1: Q169 V154
Posts: 2,261
Kudos: 3,297
Kudos
Add Kudos
Bookmarks
Bookmark this Post
User avatar
Abhishek009
User avatar
Board of Directors
Joined: 11 Jun 2011
Last visit: 02 Oct 2024
Posts: 6,014
Own Kudos:
4,948
 [4]
Given Kudos: 463
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 6,014
Kudos: 4,948
 [4]
Kudos
Add Kudos
4
Bookmarks
Bookmark this Post
stonecold
if P represents the number of prime numbers between 1 and 102 then what is the value of P?
[A] 25
26
[C] 27
[D] 28
[E] 29

All prime numbers except 2 and 3 can be expressed as -

6n + 1

and

6n - 1


Find the value of n -

n can be 100/6 = 16

Now form a table -

Attachment:
Capture.PNG
Capture.PNG [ 7.95 KiB | Viewed 4376 times ]

So we have 23 numbers between 5 to 97 and 3 more numbers (2, 3 and 101 )

[b]Hence total we have 26 numbers in the given range... :-D :lol: :x
User avatar
stonecold
Joined: 12 Aug 2015
Last visit: 09 Apr 2024
Posts: 2,261
Own Kudos:
3,297
 [1]
Given Kudos: 893
GRE 1: Q169 V154
GRE 1: Q169 V154
Posts: 2,261
Kudos: 3,297
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Abhishek009
stonecold
if P represents the number of prime numbers between 1 and 102 then what is the value of P?
[A] 25
26
[C] 27
[D] 28
[E] 29

All prime numbers except 2 and 3 can be expressed as -

6n + 1

and

6n - 1


Find the value of n -

n can be 100/6 = 16

Now form a table -

Attachment:
Capture.PNG

So we have 23 numbers between 5 to 97 and 3 more numbers (2, 3 and 101 )

[b]Hence total we have 26 numbers in the given range... :-D :lol: :x


Excellent Solution...!!
Unfortunately 5 kudos limit has been already surpassed.

StoneCold
User avatar
Abhishek009
User avatar
Board of Directors
Joined: 11 Jun 2011
Last visit: 02 Oct 2024
Posts: 6,014
Own Kudos:
4,948
 [1]
Given Kudos: 463
Status:QA & VA Forum Moderator
Location: India
GPA: 3.5
WE:Business Development (Commercial Banking)
Posts: 6,014
Kudos: 4,948
 [1]
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
stonecold

Excellent Solution...!!
Unfortunately 5 kudos limit has been already surpassed.

StoneCold

A different approach without use of 6n+1 and 6n -1

Units digit of a prime number except 2 will always be odd ( 1,3 , 5 , 7 , 9 )

So start working around.

01 - 09 = 2, 3 ,5 , 7
10 - 19 = 11, 13 , 17 , 19
20 - 29 = 23 , 29
30 - 39 = 31 , 37
40 - 49 = 41 , 43 , 47
50 - 59 = 53 , 59
60 - 69 = 61 , 67
70 - 79 = 71 , 73 , 79
80 - 89 = 83 , 87 , 89
90 - 99 = 97
100 - 102 = 101

Count you will get 26 Prime numbers

[b]stonecold
no issues Austin Bro :-D :lol: , the satisfaction of helping someone > Kudos!! ( Expression in Mathematical form because I am posting in Quants Section ) :lol:


Would love to have someone with any alternative solution to the same question, indeed its a beautiful question.
User avatar
mikemcgarry
User avatar
Magoosh GMAT Instructor
Joined: 28 Dec 2011
Last visit: 06 Aug 2018
Posts: 4,485
Own Kudos:
Given Kudos: 130
Expert reply
Posts: 4,485
Kudos: 29,380
Kudos
Add Kudos
Bookmarks
Bookmark this Post
stonecold
Can you please post a question based on odds are prime except the multiple of 5 are prime between 100 and 110, as is true between 10 and 20. This is also true between 190 and 200.
Sounds very interesting.
Do share the link if it already exists.
Thanks
Stone Cold
Dear Stone Cold,
My friend, I was inspired by this question and this discussion, and I posted a related question here:
how-many-integers-n-are-prime-numbers-in-the-range-200-n-217055.html
That one can be solved very systematically without a calculator.
Mike :-)
User avatar
stonecold
Joined: 12 Aug 2015
Last visit: 09 Apr 2024
Posts: 2,261
Own Kudos:
Given Kudos: 893
GRE 1: Q169 V154
GRE 1: Q169 V154
Posts: 2,261
Kudos: 3,297
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Abhishek009
stonecold

Excellent Solution...!!
Unfortunately 5 kudos limit has been already surpassed.

StoneCold

A different approach without use of 6n+1 and 6n -1

Units digit of a prime number except 2 will always be odd ( 1,3 , 5 , 7 , 9 )

So start working around.

01 - 09 = 2, 3 ,5 , 7
10 - 19 = 11, 13 , 17 , 19
20 - 29 = 23 , 29
30 - 39 = 31 , 37
40 - 49 = 41 , 43 , 47
50 - 59 = 53 , 59
60 - 69 = 61 , 67
70 - 79 = 71 , 73 , 79
80 - 89 = 83 , 87 , 89
90 - 99 = 97
100 - 102 = 101

Count you will get 26 Prime numbers

[b]stonecold
no issues Austin Bro :-D :lol: , the satisfaction of helping someone > Kudos!! ( Expression in Mathematical form because I am posting in Quants Section ) :lol:


Would love to have someone with any alternative solution to the same question, indeed its a beautiful question.


Kudos Visible ..!!
:)
User avatar
bumpbot
User avatar
Non-Human User
Joined: 09 Sep 2013
Last visit: 04 Jan 2021
Posts: 35,789
Own Kudos:
Posts: 35,789
Kudos: 929
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
Moderator:
Math Expert
97825 posts